1. Field of the Invention
The present invention relates to micro probes and more particularly, to an elastic micro probe for use as a circuit connection interface. The invention relates also to the fabrication of the elastic micro probe.
2. Description of the Related Art
When testing high-density or high-speed electrical devices (for example, LSI or VLSI circuits), a probe card having a big amount of elastic micro contacts (probes) shall be used. By means of the resilient and electrically conductive material property of the elastic micro probes, the probe card is used as an electric connection medium between the test apparatus and the device to be tested, for example, an LSI chip, VLSI chip, semiconductor wafer, semiconductor chip, semiconductor package, or printed circuit board. Elastic micro contacts can also be used as lead wire means for an IC package. For easy understanding of the present invention, elastic micro contacts are described as probes for probe cards.
Conventionally, elastic micro probes, more particularly upright probes are made by means of forging technology or micro electromechanical technology.
FIG. 1 shows an elastic probe 5 according to the prior art. This structure of elastic probe 5 is comprised of a plurality of parts that are separately made through a precision manufacturing process and then assembled together. Through a precision manufacturing process, the parts can be made subject to the desired precision. However, it is complicated to assemble the precision parts. Because the spring member for this elastic probe is a thin and elongated metal wire member, it has a low stability. When compressed, the spring member may be biased to rub against the peripheral wall, resulting in unnecessary wearing and tip contact instability.
In order to eliminate the problem of complicated assembly process, there are manufacturers who employ a semiconductor integration manufacturing process to fabricate spring probes directly from a substrate. This semiconductor integration manufacturing process eliminates the assembly process. FIG. 2a shows a spring probe 1 made according to this semiconductor integration manufacturing process. According to this design, the spring body 3 of the spring probe 1 blocks the solder joint 2 (see FIG. 2a). When damaged, the spring probe 1 is not replaceable. By means of the spring body 3 between the top tip 4 and the bottom solder joint 2, the spring probe 1 is compressively deformable upon a pressure. The H (height) to W (width) ratio of a spring probe is normally below 3.7. FIG. 2b shows a spring probe of H/W<3.7 compressed by a downward force F. FIG. 2c shows a spring probe of H/W>3.7 compressed by a downward force F. As shown in FIG. 2c, the spring probe buckles when being compressed. In order to prevent excessive deformation, the H (height) W (width) ratio of a spring probe must be limited to a certain level. When reducing the width of the spring probe, the height of the spring probe must be relatively reduced. In this case, the amount of elastic deformation the spring probe itself can provide is relatively reduced, i.e., the power of the spring probe to compensate flatness error relative to the surface condition of test sample and the limitation of mechanical leveling control is relatively reduced. Following the development of miniaturized semiconductor and package technology, this design of spring probe cannot meet actual requirements. Further, the alignment error of the multilayer structure between the solder joint 2 and the tip 4 cannot assure accurate positioning of the tip during bonding. Further, because the spring probe is completely exposed to the outside, it tends to be damaged.